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Detection of Aspergillus Flavus and Aflatoxins in Cotton and Corn by Ultraviolet Fluorescence¹

ABSTRACT

A 1954 report from the Beltsville Agricultural Research Center recorded the observation of a bright greenish-yellow fluorescence or "BGYF" in raw cotton (Gossypium hirsutum L.) fiber and linked it to a previously unrecognized boll rot caused by Aspergillus flavus Link ex Fr.). Nine surveys employing the fluorescence as a detection device on U.S. cotton fiber produced during 1957 to 1981 showed this boll rot mostly in especially hot growing areas in southern California, Arizona, and Texas. The BGY-fluorescing substance was produced in pure-culture incubations of A. flavus on live never-dried cotton fiber from unopened bolls. Evidence indicated it is caused by interaction between kojic acid from the fungus and peroxidase from the fiber. The fluorescence in field-grown lint or seed-fuzz is often accompanied by variable but generally high levels of A. flavus-produced aflatoxins in the seeds bearing such fiber; presence of the fluorescence may be used as a presumptive test for aflatoxins. A 1968 report from Beltsville showed that the BGY fluorescence can also be generated by A. flavus in pure culture on live milk-stage corn (Zea mays L.) kernels. Others later observed it in corn in the field and used it in corn-aflatoxin investigations. A rapid presumptive test for aflatoxins in commercial corn, based on the BGY fluorescence, has been extensively used. Aspergillus flavus field infection and the BGY fluorescence in cotton and corn are influenced by the semithermophillic, semixerophytic, and wound-parasitic characteristics of the fungus.

Key Words: boll rot • kojic acid • peroxidase

¹ Contribution from the Beltsville Agric. Res. Center, USDA, Beltsville, MD 20705.

² Microbiologists, USDA, Beltsville.

Received for publication May 12, 1983.